In a reciprocating engine (a reciprocating piston engine) except for some 2-cycle engines, there are provided intake valves and exhaust valves that open and close in synchronization with the rotation of the crank shaft. In this kind of reciprocating engine, the movement of the cam shaft that rotates in synchronization with the rotation of the crank shaft (½ the rpm in the case of a 4-cycle engine) is transmitted to the intake valves and the exhaust valves by rocker arms, and causes the intake valves and exhaust valves to move in a reciprocating motion in the axial direction thereof.
Conventionally, castings (iron castings or aluminum die-castings) were used for the rocker arm assembled into the valve operating mechanism of this kind of engine. Furthermore, in recent years, manufacturing the rocker arm by press-processing a metal plate such as a steel plate, has been consider d, and is being performed to some extent. However, in the case of the rocker arm of such a casting or the rocker arm made from a metal plate, the time required for the fabricating operation is long, and waste of material is significant, so that there is a problem of an increase in cost.
To address this, as disclosed in Japanese Patent Application Publication No. H10-328778, a method of manufacturing a rocker arm has been proposed wherein cold forging is applied to a blank obtained by cutting a metal wire rod to a predetermined length. According to Japanese Patent Application Publication No. H10-328778, in the case of making the rocker arm by applying cold forging to the blank made from a metal wire rod, this can be made to high accuracy without the occurrence of cracking, so that work efficiency can be favorable. Moreover, in the case where the rocker arm is made by this cold forging, then compared to the case where this is made by hot forging, the form accuracy and the dimensional accuracy can be increased. FIG. 22 to FIG. 28 illustrate an invention related to the method of manufacturing a rocker arm disclosed in Japanese Patent Application Publication No. H10-328778. This rocker arm manufacturing method is described in detail in Japanese Patent Application Publication No. H10-328778, and hence is only briefly described here. As shown in FIG. 22, a rocker arm 1 has a pair of side wall sections 2 that are nearly parallel with each other, and a first connecting section 3 and a second connecting section 4 that connect the lengthwise opposite ends of the two side wall sections 2. Of these first connecting section 3 and second connecting section 4, the first connecting section 3 has a first engagement section 6 for abutting against the base end of a valve body, and the second connecting section 4 has a second engagement section 7 for abutting against a tip end of a rocking support member such as a lash adjuster.
Furthermore, while not disclosed in Japanese Patent Application Publication No. H10-328778, in the case of the actually used rocker arm, a pair of holes are formed concentric with each other in the lengthwise middle portion of the two side wall sections 2, and opposite ends of a support shaft for rotatably supporting a roller which is engaged with a cam, are freely supported in these two holes.
The operation for making such a rocker arm 1 is carried out as follows. At first, as shown in FIG. 23, an end of a steel wire rod 9 which is wound in a coil on a rotating support apparatus 8, is drawn out by a roller type wire feed mechanism 11 which is provided on a cold forge forming machine 10, and is guided into the cold forge forming machine 10. The cross-section shape of the metal wire rod 9 is rectangular. Furthermore, by previously pickling the metal wire rod 9 in a lubrication liquid tank of a zinc phosphate or the like, a lubricating film layer is formed on the outer surface of the metal wire rod 9. Then, as a first step, as shown in FIG. 24, the metal wire rod 9 is cut to a predetermined length in a cutting mechanism 12 provided in the cold forge forming machine 10, to thereby make a blank 13 of a rectangular solid. The cold forge forming machine 10 is referred to as a horizontal multistage forging forming machine, and comprises a die block 14 secured to the inside, and a ram 15 which reciprocates in the horizontal direction so as to approach and separate (move apart and close) with respect to the die block 14. In the die block 14, a plurality of fixed dies 16a to 16d are arranged spaced apart in the horizontal direction. Furthermore, on part of the ram 15, facing the fixed dies 16a to 16d, a plurality of moveable dies 17a to 17d are arranged through the medium of respective die holders 18a to 18d. At the sections where the fixed dies 16a to 16d and the moveable dies 17a to 17d are arranged, there are respectively provided; a first forging station 19, a first punching station 20, a second forging station 21, and a second punching station 22. The rectangular solid blank 13 obtained by the first step is supplied to the first forging station 19 while changing the direction of the blank 13 through 90 degrees, by means of a material rotation feed mechanism 23 provided in the cold forge forming machine 10.
At the first forging station 19, as a second step, as shown in FIG. 25, the blank 13 is subjected to cold forging by punching the blank 13 in the horizontal direction into the fixed die 16a by the moveable die 17a, to thereby make a first intermediate blank 24 having a rough shape and dimension of the rocker arm 1. This first intermediate blank 24 comprises a pair of side wall sections 2 (FIG. 22) and a base 51 which connects the widthwise middle portions of the two side wall sections 2, giving a cross-section H-shape. A burr 25 is formed around the entire periphery of the first intermediate blank 24 on the outer peripheral face of the thickness direction middle portion. Since previously a lubrication film layer is formed on the outer peripheral face of the blank 13 which has been subjected to this cold forging, the friction acting between the inside face of the fixed die 16a and the moveable die 17a, and the outside face of the blank 13 is kept to a minimum. Furthermore, by means of this configuration, the forming workability and the shape accuracy of the first intermediate blank 24 can be made good. The first intermediate blank 24 which is made in such a second step is taken out from between the fixed die 16a and the moveable die 17a, and is supplied to a first punching station 20 as shown in detail in FIG. 26.
In this first punching station 20, as a third step, as shown in FIG. 26, of the first intermediate blank 24, a main body portion except for the burr 25 is clamped between the tip end face of a cylindrical extrusion member 27 provided inside a bore 26 of a fixed die 16b, and the tip end face of a cylindrical moveable die 17b. Then by extruding the main body portion inside the bore 26, the burr 25 is removed by the rim portion of the open end of the bore 26. Simultaneous with this, the middle portion of the base 51 (FIG. 25) provided on the first intermediate blank 24 is punched by a hole punch 28 provided on the inside of the cylindrical extrusion member 27, to thereby make a second intermediate blank 30 having a hole 29. By forming this hole 29, both the first and second connecting sections 3 and 4 that connect the lengthwise opposite ends of the pair of side wall sections 2 (FIG. 22) are formed on the second intermediate blank 30. The second intermediate blank 30 obtained by this third step is taken out from between the fixed die 16b and the moveable die 17b, and is supplied to the second forging station 21 as shown in detail in FIG. 27.
In the second forging station 21, as a fourth step, the second intermediate blank 30 is subjected to cold forging by punching the second intermediate blank 30 in the horizontal direction into the fixed die 16c by the moveable die 17c, to thereby make a third intermediate blank 31 having dimensions and shape close to the finished product. At this time, respective burrs 25a and 25b are formed on the outer peripheral face of the thickness direction middle portion of the third intermediate blank 31, and the inner peripheral face of the hole 29. In carrying out this cold forge forming, since the lubrication film layer is formed beforehand on the outer face of the second intermediate blank 30, the friction acting between the inner face of the fixed die 16c and the movable die 17c, and the outer face of the second intermediate blank 30 is kept to a minimum. By means of this configuration, the forming workability and the form accuracy of the third intermediate blank 31 can be made good. Once this fourth step is completed, the third intermediate blank 31 is taken out from between the fixed die 16c and the movable die 17c, and this third intermediate blank 31 is supplied to the second punching station 22 as shown in detail in FIG. 28.
At the second punching station 22, as a fifth step, as shown in FIG. 28, similar to the case of the third step, the burr 25a formed on the outer peripheral face of the third intermediate blank 31 is removed. Simultaneous with this, the burr 25b formed on the inner peripheral face of the hole 29 of the third intermediate blank 31 is also removed, to thereby give the finished product of the rocker arm 1. This rocker arm 1 is taken out to a predetermined position, from between the fixed die 16d and the moveable die 17d of the second punching station 22 by, for example, an ejection chuck (not shown in the figure). Furthermore, although not disclosed in Japanese Patent Application Publication No. H10-328778, in the case of the actually used rocker arm, a separate processing machine is used to carry out a hole forming process in order to form a pair of circular holes at mutually matching positions in the middle portions of the respective side wall sections 2 (FIG. 22).
When the rocker arm 1 is manufactured by the multistage cold forging machine as with the method of manufacturing a rocker arm disclosed in Japanese Patent Application Publication No. H10-328778, the time required for the manufacturing operation can be shortened to some extent, so that work efficiency can be made good, thus facilitating a reduction in the cost of the rocker arm 1. Furthermore, in the manufacturing method, since the movable dies 17a to 17d are moved in the horizontal direction, then compared to the case where the forging operation is carried out by moving the movable dies in the vertical direction, the load applied to the drive mechanism for moving the movable dies 17a to 17d back and forth can be reduced. Therefore, speeding up of the cold forging operation for obtaining the rocker arm 1 can be facilitated.
However, in the rocker arm disclosed in Japanese Patent Application Publication No. H10-328778, and the manufacturing method therefor, there is further room for improvement in the following points.
(1) The hole 29 which is formed by applying the punching process to the first intermediate blank 24 in order to provide the first and second connecting sections 3 and 4, is located at the approximately middle portion in relation to the widthwise direction of the pair of side wall sections 2. Moreover, since this hole 29 is formed by the punching process, the inside peripheral face thereof becomes a rough sheared face (fractured face). Therefore, in a condition where the cam follower is constructed by assembling the roller into the rocker arm 1, the opposite end faces of the roller are likely to come in contact with this sheared face (fractured face). When in this manner the opposite end faces of the roller come in contact with the sheared face (fractured face), it is difficult to smoothly rotate the roller, thus becoming an impediment to performance improvement of an engine incorporating the rocker arm 1. Furthermore, in the case where the opposite end faces of the roller come in contact with the sheared face (fractured face), the opposite end faces of the roller are abnormally worn, and abrasion powder which is produced by wear at the contact portion enters into the space between the component members of the engine, so that there is a likelihood of performance deterioration of the engine.
(2) There is still room for improvement from the point of weight lightening. That is, in the case of the rocker arm 1 disclosed in Japanese Patent Application Publication No. H10-328778, a starting position P of one lengthwise end rim (the lower end rim in FIG. 22) of the side wall sections 2 on one side (the left side in FIG. 22(a)) of the first connecting section 3 is close to the one lengthwise end rim (the lower end rim in FIG. 22) of the rocker arm 1. Therefore, the lengthwise dimension of the side wall sections 2 becomes large, so that the volume of the rocker arm 1 becomes unnecessarily bulky, becoming a cause of increase in the weight of the rocker arm 1. When in this manner the weight of the rocker arm 1 is increased, this becomes a cause of a drop in performance, such as the output performance, of an engine having this rocker arm 1.
(3) In both of the second and fourth steps which are forging processes for obtaining the rocker arm 1, the cold forging operation is applied to the blank 13 (or the second intermediate blank 30) by pressing the rectangular solid blank 13 (or the second intermediate blank 30) from opposite sides in the perpendicular direction (the thickness direction of the base 51 or the connecting sections 3, 4) with respect to the axial direction (lengthwise direction), being mutually the same directions. Therefore, in the second and fourth steps, excessive stress is likely to concentrate in one part of the blank 13 and the second intermediate blank 30 which corresponds to the same portion of the obtained rocker arm 1, so that in the obtained rocker arm 1, it is difficult to sufficiently maintain the strength.
Furthermore, the blank 13 is a rectangular solid, and the cross-section area in relation to the axial direction (lengthwise direction) is the same. On the other hand, in the second intermediate blank 30, the cross-section area in the axial direction is not uniform (changes significantly). Therefore, the second intermediate blank 30 cannot be obtained by directly cold forging from the blank 13. The second intermediate blank 30 must be made by cold forging the first intermediate blank 24 with the accompanying burr 25, and then removing this burr 25 in a subsequent punching process.
When the cold forging operation is carried out in this manner with the accompany burr 25, the fiber flow, which is the flow of the internal fibrous structure, of the second intermediate blank 30, is newly created along the flow direction of the burr 25. Together with this, the fiber flow formed in the original first intermediate blank 24 is disturbed at the burr 25 portion and becomes discontinuous. Moreover, by removing the burr 25 in a subsequent process, the fiber flow of this portion is parted (cut). If the fiber flow is parted in this way, the strength of the finished product (article) of the obtained rocker arm 1 tends to decrease. Furthermore, when the burr is parted, a sheared face or fractured face accompanying this is produced, so that there is a possibility of defects occurring. Moreover, this becomes a cause of deterioration in form accuracy. Also, since the forging load is increased, equipment having a large forging capacity is necessary. Furthermore, material loss is naturally increased due to the burr 25, becoming a cause of an increase in cost.
In the case of the method of manufacturing a rocker arm disclosed in Japanese Patent Application Publication No. H10-328778, the same operation is repeated in the fourth and fifth steps. That is, after executing cold forging with the accompanying burrs 25a and 25b, these burrs 25a and 25b are removed. Therefore a drop in strength and deterioration in precision of the product is likely to occur even more.
Furthermore, of the burrs 25, 25a, and 25b formed accompanying the cold forging, the burrs (outer burrs) 25 and 25a which occur on the outer peripheral side are formed on the surroundings, and hence the volume is increased. Therefore, compared to the burr (inner burr) 25b which occurs on the inner peripheral side, the loss of material is remarkably increased. Regarding the inner burr 25b, preferably this is not produced. However in the case where this is unavoidable, it is necessary to form this on a portion where it has minimal influence on the use of the finished product of the rocker arm 1.
(4) In the case of the rocker arm 1 for actual use, a circular hole for supporting the opposite ends of the support shaft with the roller supported on the middle portion, is formed in each of the side wall sections 2 (FIG. 22). However, in the case where these circular holes are simple cylindrical surfaces over their entire length, the opposite ends of the support shaft cannot be securely engaged with sufficient engagement strength in these circular holes. Therefore, it is difficult to sufficiently ensure the endurance of a cam follower constructed with the roller incorporated into the rocker arm 1. That is to say, in the case where the circular holes are simply cylindrical surfaces as described above, the opposite ends of the support shaft must be secured in these circular holes by a simple press fit, or by bonding or by a shrink fit or the like, so that it is difficult to sufficiently ensure the endurance of the cam follower. In the case of the method of manufacturing a rocker arm disclosed in Japanese Patent Application Publication No. H10-328778, there is no disclosure of forming the circular holes in the respective side wall sections 2, and of course improvement in the engagement strength of the opposite ends of the support shaft with respect to these circular holes is not considered.
(5) When cold forging is carried out at the second forging station 21 in order to form the first and second engagement sections 6 and 7 (FIG. 22) for abutting against the valve body or the rocking support member, no consideration is given to providing a run-off for the excess thickness portion of the material, close to the first and second engagement sections 6 and 7, at one part of the second intermediate blank 30. Therefore, in order to form the first and second engagement sections 6 and 7, the excess thickness portion of the second intermediate blank 30 effectively cannot be escaped, and the form accuracy and the dimensional accuracy of the first and second engagement sections 6 and 7 cannot be made good. Therefore, it is difficult to accurately engage the valve body or the lash adjuster at a predetermined position of the rocker arm 1.
From the above points, in the rocker arm and the manufacturing method therefor disclosed in Japanese Patent Application Publication No. H10-328778, there is room for improvement in the performance and endurance of an engine incorporating the obtained rocker arm.
Consequently, in the rocker arm and manufacturing method therefor of the present invention, in the case where the rocker arm is made by applying cold forging to a blank made of a metal wire rod, it is an object to improve the performance of an engine incorporating this rocker arm.
Furthermore, in the case of the method of manufacturing a rocker arm disclosed in Japanese Patent Application Publication No. H10-328778, the burrs 25, 25a, and 25b are formed in one part of the first intermediate blank 24 and the third intermediate blank 31. Therefore, the material cost is increased by the amount of these burrs 25, 25a, and 25b. In particular, in the case of the method of manufacturing a rocker arm disclosed in Japanese Patent Application Publication No. H10-328778, the volume of these burrs 25, 25a, and 25b is large. Next the reason for this is described. In the rocker arm 1 obtained by the method of manufacturing a rocker arm disclosed in Japanese Patent Application Publication No. H10-328778, the pair of side wall sections 2 are formed in an approximate rhomboid shape. Accompanying this, the first intermediate blank 24 which is manufactured in the second step at the first forging station 19, has an H-shape cross-section, and the widthwise dimension of the portion which is to become the side wall sections 2 (refer to FIG. 18) is formed so as to become smaller from near the lengthwise center towards the lengthwise opposite ends. On the other hand, the blank 13 which is to be subjected to cold forging in the second step, is a rectangular solid in which the area of the cross-section shape in relation to a direction perpendicular to the axial direction (the lengthwise direction) does not change along the entire axial length. That is to say, in the case of the method of manufacturing a rocker arm disclosed in Japanese Patent Application Publication No. H10-328778, in spite of the fact that the cross-section area of the first intermediate blank 24 which is to be obtained by the cold forging changes in relation to the lengthwise direction, the blank 13 which is to be subjected to cold forging is a rectangular solid in which the cross-section area thereof does not change along the entire axial length. When in this way the shape to be obtained by cold forging, and the shape of the blank 13 to be subjected to this cold forging are very different, the volume of the burrs 25, 25a and 25b to be removed in the later process becomes large.
A process accompanied by the positive outputting of the burr can be easily conceived by one skilled in the art, and comparatively easily executed. That is to say, the shape and dimension of the finished product largely depends on the shape and dimensions of the die for processing the blank or the intermediate blank which is to give the finished product. Consequently, if the volume of the blank or the intermediate blank is made slightly larger than the volume of the finished product to be obtained, the processing for obtaining the finished product can be easily performed, and the surplus portion produced at the time of each process can be produced as the burr, and cut-off in the later process.
However, if a lot of burr to be removed is produced in the cold forging then not only is a separate process for removing this burr necessary, but also this becomes a cause for an increase in material cost. Therefore, in the case of the method of manufacturing a rocker arm disclosed in Japanese Patent Application Publication No. H10-328778, there is still room for reducing the cost of the rocker arm.
Patent Document 1: Japanese Patent Application Publication No. H10-328778